1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to a method and system for transmitting/receiving data in a Multi-Input Multi-Output (MIMO) communication system.
2. Description of the Related Art
The key issue in communication is how efficiently and reliably is it possible to transmit data through a channel. In the next generation multimedia communication system, there is ongoing research to meet the need for a high-speed communication system capable of processing and transmitting a variety of information such as image and radio data, beyond the early voice-oriented service, because it is essential to increase the system efficiency using a channel coding scheme suitable for the system.
However, a wireless channel environment in the communication system, unlike the wired channel environment, suffers inevitable errors due to several factors, such as multipath interference, shadowing, radio attenuation, time-varying noise, interference, fading, and the like, and occurrence of the errors causes information loss. The information loss brings considerable distortion on actual transmission signals, causing a reduction in the entire performance of the communication system. Generally, in order to reduce information loss, various error control techniques are used according to channel characteristics to increase system reliability, and the most typical error control technique uses error correction codes.
Further, in order to remove communication instability due to fading, a diversity scheme is used, and the diversity scheme is roughly classified into a time diversity scheme, a frequency diversity scheme, and an antenna diversity scheme, i.e. space diversity scheme.
The antenna diversity scheme, a scheme using multiple antennas, is classified into a reception antenna diversity scheme using a plurality of reception antennas, a transmission antenna diversity scheme using a plurality of transmission antennas, and a Multiple Input Multiple Output (MIMO) scheme using a plurality of reception antennas and a plurality of transmission antennas.
In the MIMO communication system, Space-Time Coding (STC) determines what data it will transmit for each of the plurality of transmission antennas, and each of the reception antennas receives the signal transmitted from each of the transmission antennas and performs STC decoding thereon. The STC coding is implemented with a space-time transmit diversity technique for encoding the same data in different formats to transmit the same data via different transmission antennas, or a spatial multiplexing technique for transmitting different data via different transmission antennas.
Generally, in the spatial multiplexing technique, an STC-coded signal is decoded at a receiver using a joint or separate detection scheme. The joint detection scheme should take into account not only the signal transmitted from one transmission antenna, but also the signals transmitted from other transmission antennas. Due to this characteristic, multiplexing techniques such as Minimum Mean Square Error (MMSE), and Zero-Forcing (ZF)-based Joint-Channel Diagonalization (JCD), are well known as a multiplexing scheme for using the spatial multiplexing MIMO communication system.
Among the multiplexing techniques, the JCD-based multiplexing technique obtains higher data throughput compared with the MMSE-based multiplexing technique at a high Signal-to-Noise Ratio (SNR). On the contrary, at a low SNR, the MMSE-based multiplexing technique can obtain higher throughput performance compared with the JCD-based multiplexing technique. However, because the communication system generally multiplexes data using one multiplexing technique, it cannot use a multiplexing technique corresponding to a varying SNR in a time-varying wireless channel environment, causing performance degradation. In addition, the MMSE and JCD-based multiplexing techniques considerably increase in the system complexity, as the number of transmission antennas and the number of reception antennas increase.